This invention relates to an integrated circuit package, and more particularly to an integrated circuit package having good heat dissipation properties by bonding a heat sink such as a cooling fin to a ceramic package.
Integrated circuit packages (i.e. packaged integrated circuit devices) comprising an insulating substrate made of ceramics, a cap, and a sealing material for sealing the cap and the insulating substrate to form a small hermetic chamber which encloses at least one semiconductor element, lead members introduced from the outside of the chamber and wires electrically connecting the semiconductor element and the lead members, and a cooling fin affixed to a rear surface of the insulating substrate are widely used today.
A problem arised by using such ceramic packages is very poor heat dissipation properties when heat is produced in the semiconductor element. This is a large obstacle to making semiconductor elements larger in capacity, higher in integration and smaller in size. Therefore, it is required in the integrated circuit packages that ceramics used as insulating substrates for mounting one or more semiconductor elements thereon have excellent electrical insulating properties as well as excellent thermal conductivity. It is also desired that a material used for the insulating substrate has a thermal expansion coefficient very close to that of silicon semiconductor and large mechanical strength.
As an insulating substrate satisfying the abovementioned conditions to some extent, there is used now an alumina sintered body. But the alumina sintered body has a thermal conductivity of as low as 0.05 cal/cm.sec..degree.C. Therefore, the alumina sintered body is not a preferable material from the viewpoint of heat dissipation properties of the semiconductor element.
On the other hand, in order to improve the heat dissipation properties of a semiconductor element enclosed in a ceramic package from the viewpoint of structure, a process is proposed wherein a semiconductor 1 is disposed on a copper stud 31 extending out of a package through an insulating substrate 4 as shown in FIG. 1 [IEEE TRANSACTIONS ON COMPONENTS, HYBRIDS, AND MANUFACTURING TECHNOLOGY Vol. CHMT.-4, No. 2, 166(1981)]. In FIG. 1, in the package comprising the substrate 4, a cap 5 and a sealing material 6, the semiconductor 1 is bonded to the copper stud 31 via a supporting plate 32 made of molybdenum by solder layer 7 in order to relax stress caused by a difference in thermal expansions of the semiconductor and the copper stud. The semiconductor element 1 is electrically connected to a terminal of a lead piece 3 adhered to the substrate 4 by bonding wires 2. The heat produced in the semiconductor element 1 is conducted to the outside of the package via the supporting plate 32 and the copper stud 31 and further is dissipated by a cooling fin 9. In such a structure, since all the heat transfer path from the semiconductor 1 to the cooling fin 9 is made of a metal excellent in thermal conductivity, there can be obtained an integrated circuit package having high heat dissipation properties. But this process has defects in that (1) assembly steps increase due to an increase of the number of parts and a complicated structure, and (2) since parts made of copper, molybdenum or the like having larger specific gravities are used, the weight of products increases to make the disposal of the products on printed wiring boards and the like troublesome.
In order to overcome such defects, a packaged integrated circuit device is proposed which uses an insulating substrate made of silicon carbide ceramic having a high thermal conductivity and a thermal expansion coefficient very close to that of silicon in order to make the heat dissipation properties better (U.S. patent application Ser. No. 572,518). But according to this packaged integrated circuit device, since a cooling fin made of aluminum or its alloy is bonded to a rear surface of the insulating substrate made of silicon carbide ceramic by using an epoxy resin or the like resin adhesive having a higher Young's modulus when formed into a film, there arises a problem in that cracks are produced on a glass layer in the glass sealed package when subjected to cooling and heating cycles.